Ligand-mediate exciton allocation enables efficient cluster-based white light-emitting diodes via single and heavy doping

Despite potential in high-resolution and low-cost displays and lighting, multi-doping structures and low concentrations (<1%) limit repeatability and stability of single-emissive-layer white light-emitting devices. Herein, we report a singly doped white-emitting system of blue thermally activated delayed fluorescence host matrix (CzAcSF) doped by yellow Cu4I4 cluster ([tBCzDppy]2Cu4I4). CzAcSF:x% [tBCzDppy]2Cu4I4 films realize photo- and electro-luminescence colors from cool white to warm white at x = 20–40. The external quantum efficiency of 23.5% was achieved at x = 30, indicating the record-high efficiency among solution-processed analogs and the largest doping concentration among efficient white light-emitting devices. It shows that di(tert-butyl)carbazole moieties in [tBCzDppy]2Cu4I4 provide high-lying excited energy levels at~2.6 eV to mediate energy transfer from CzAcSF (2.9 eV) to coordinated Cu4I4 (2.2 eV). Our results demonstrate the antenna effect of ligands on optimizing charge and energy transfer in organic-cluster systems and superiority of white cluster light-emitting diodes in practical applications.

Reviewer #3 (Remarks to the Author): In this work, the authors selected yellow-emitting copper clusters and a blue TADF host CzAcSF to form the white-emitting devices.Although there were reports of white OLEDs and PeLEDs, I agree with the authors that clusters based on eco-friendly cheap metals can provide the important alternatives for the large-scale applications, since the high rigidity of clusters can limit the J-T distortion of mononuclear complexes.I noticed that Yao et al. recently reported a warm whiteemitting device of Cu2I2 clusters with broad emissions, which was obviously different to this work regarding to material design and photophysical investigation (Nat Photon 18, 200-206 (2024)).The performance reported in this work was also improved.What I am interested in is the heavy doping for realizing white emission reported in this work, which was thoroughly different to all previously reported white-emitting systems.This finding may discover one advantage of cluster emitters.The authors organized the experiments and investigations carefully to figure out the fundamentals behind the unique photophysical processes in CzAcSF:Cu4I4 cluster films and the key factors of carrier and energy transfer.The EQE of 23.5% achieved at 30% doping concentration by the solution-processed devices indicated the potential of white cluster light-emitting devices.Therefore, I would like to recommend the publication of this work in Nature Communications.Some minor revisions would be necessary: 1.It was a good idea to use copper clusters as long-wavelength emitters for binary white-emitting systems, considering the sustainability and low cost of copper, since previous works were based on noble-metal complexes containing iridium and platinum, etc.For example, Forrest et al. reported the white OLEDs based on Ir(ppy)3 and PQIr (Nature 440, 908-912 (2006)).But, I still wonder are there any other fundamental advantages of the copper clusters for white-emitting applications.
2. On page 7, paragraph 3, the authors claimed that the emission duration of [Dppy]2Cu4I4 film decreased more significantly at higher temperatures, in comparison to [tBCzDppy]2Cu4I4 film, because the rigid and bulky tBCz groups inhibited the quenching effect.Since tBCz groups also modified the solubility and film formability, the film morphology of [tBCzDppy]2Cu4I4 might be different with that of [Dppy]2Cu4I4, the authors are suggested to add and discuss the time decay curves of the clusters in powder.
3. On page 8, paragraph 3, CzAcSF:x% [tBCzDppy]2Cu4I4 film exhibited dual-peak emission, and the relative intensity of yellow was proportional to x%, resulting in emission color change from cool white to warm white.Since the authors claimed the importance and limitation of host-cluster energy transfer, the dependence of emission color on the smaller x% change would reflect the improved energy transfer from CzAcSF to [tBCzDppy]2Cu4I4.
4. The authors claimed that different to Dppy, tBCzDppy may have the TADF characteristics due to its donor-acceptor structure.I suggest them to compare the photophysical properties of Dppy and tBCzDppy to support it, especially temperature-related decays.
5. On page 10, line 305, "At x =30, color rendering index (CRI) can reach to 81" was different to the CRI value of 72 in Table S3.The authors should carefully check the data.
Reviewer #4 (Remarks to the Author): This work reported a novel single-doped white light emission system based on blue TADF host (CzAcSF) and yellow Cu4I4 cluster dopant ([tBCzDppy]2Cu4I4).The EL emission changed from cold white to warm white through tuning doping concentration of 20-40%, owing to the limited hostcluster energy transfer.When the doping concentration was 30%, the EQE of the solutionprocessed devices reached 23.5%.The advantage of singly cluster doped white-emitting device in heavy doping is important for applications.The authors made a systematic investigation and rational explanation on the improved energy transfer between cluster and CzAcSF, through highlying excited states from carbazole moieties.The authors demonstrated the main conclusions with solid evidences, which would be important to understand the unique excited-state properties of cluster emitters.This work can be published in Nature Communications after suitable revisions.
1.I have noticed that in recent years, there have been some works used clusters as emissive layers to prepared electroluminescent devices, most of which showed blue or yellow emissions, and the reports of white devices based on clusters were only few (Nat.Commun.2023, 14, 2901; Angew.Chem.Int.Ed. 2021, 61, e202213826).Please briefly introduce the main challenge of developing cluster based white light-emitting devices.
2. Dppy is a common ligand for cluster preparation.Wang et al prepared gold clusters based on Dppy (J.Am.Chem.Soc.2013, 135, 16184).Therefore, are there any advantages of this kind of ligands in comparison to triphenylphosphine, regarding to EL cluster design.

In Fig 2 (d)
, the time-resolved emission spectra (TRES) of PMMA : 10% cluster films revealed that the effect of phonon relaxation on [tBCzDppy]2Cu4I4 was negligible.To exclude the influence of host matrix, the temperature-dependent TRES of pure films for the clusters should be compared.

4.
The authors reported a very high EQE of 23.5% for a spin-coated white light-emitting device.Because the authors claimed host-cluster energy transfer was limited, the repeatability of the high performances was doubted.Please give the data to demonstrate the performance repeatability of the best devices.5. Please describe the synthesis details and single crystal growth approach of [tBCzDppy]2Cu4I4 in the supporting information.Response: Thanks a lot for this kind reminding!We should apologize for our carelessness.As reviewer pointed out, "yellow emissive Cu 4 I 4 " is correct.All the related expressions were revised accordingly.Thanks a lot!
Response: Thanks a lot for this kind reminding!We should apologize for our carelessness, inducing the typos, which were corrected in the revision.We further rechecked the manuscript carefully to get rid of typos and grammatical errors to our best.Thanks a lot!
Page 12, Line 369 "Copper iodide cluster synthesis".Please provide the detailed synthesis process utilized to obtain the clusters.Additionally, include characterizations of the Cu 4 I 4 clusters, including NMR spectroscopy, mass spectrometry (MS), and elemental analysis either in the main text or in the SI.
Response: Thanks a lot for this constructive comment!The descriptions of preparation procedures for the clusters were enriched in the manuscript.All the details were further described in the experimental section of Supplementary information.All the NMR and MS spectra were added in the supplementary information as Supplementary Figures S35-S40.Thanks a lot!

Revision:
The detailed synthesis process and characterization of clusters include 1 H-NMR, 13  Response: Thanks a lot for this constructive comment!We should apologize for our insufficient description.The relative equations were also added in the Supplementary Note 4. Photophysical Analysis.Thanks a lot!

Revision:
The description and related equations for calculating the transition rate constants were add : "The calculation formulas for the rate constants of prompt fluorescence (k PF ), delayed fluorescence (k DF ), singlet radiation (   ),singlet (   ) and triplet nonradiation (   ), reverse intersystem crossing (k RISC ) and intersystem crossing (k ISC ), and corresponding quantum efficiencies (ϕ) are expressed as following list: 6.
In the main text, please provide further descriptions of the reasons why the authors choose to modify the group on the ortho position of the carbon in the Dppy ligand, as well as the reason for selecting tert-butyl carbazole as the modification.
Response: Thanks a lot for this constructive comment!In our molecular design, a hole-transporting group with host characteristics would provide intermediate energy levels to support energy and charge transfer to coordination core.
Carbazole is one of the most popular functional groups widely used in hole transporting materials and host matrixes On the other hand, the ortho-substitution of tBCz not only increases steric hindrance, but also induces locally asymmetric configuration of [tBCzDppy] 2 Cu 4 I 4 , which can reduce inter-cluster interaction induced quenching.
Carbazole group at the ortho position of Dppy is the closest to the coordination core of Cu 4 I 4 .Consequently, the distance between tBCz and Cu 4 I 4 cube is only 7.5 Å, which is highlighted in Supplementary Fig. 4, and beneficial to energy and charge transfer from the peripheral ligands to the coordination core.Supplementary Fig. 4 was updated, and the detailed explanation was added in the related section.Thanks a lot! Revision:

Response:
We highly appreciate reviewer's approval on our work!We should apologize for our insufficient discussions and explanations.So, we would like to take this chance to explain the novelty and important findings of this work, especially overcoming the great challenging in efficient energy and charge transfer from TADF hosts to cluster emitters through ligand engineering.Purposeful ligand functionalization can comprehensively optimize optoelectronic properties of cluster based multicomponent systems, which would largely extend the applications of these emerging materials.
Despite the rapid development of cluster-based mono-color light-emitting diodes with external quantum efficiencies more than 20%, only few efficient white cluster light-emitting diodes were reported, mainly due to the inefficient and balanced exciton allocation between blue and yellow emitters in cluster-involved white-emitting systems, especially the uncontrollable energy transfer from blue emitters to clusters.In our previous works, we can not achieve the simultaneous emissions from both clusters and blue-emitting TADF hosts, e.g.CzAcSF, despite carefully tuning cluster concentrations (Angew.Chem.Int.Ed. 2023, 62, e202305018).Actually, until present, the excited state properties of metal haloid luminescent materials are still not clear.Copper iodide clusters exhibit completely different excited state properties from copper complexes, pure organic molecules and polymers.We believe that this work provides valuable progress in terms of luminescent mechanism.Obviously, the energy transfer and exciton allocation between hosts and cluster emitters is completely different with organic host-guest systems.Therefore, this work not only develops an effective approach to realize white emissions from cluster-based systems, but also demonstrates the feasibility and importance of ligand functionalization in modulating host-cluster energy transfer and exciton allocation in devices.These results can undoubtedly facilitate the development of cluster materials for optoelectronic applications.
The main findings in our work are as follows: (iii) Excellent EL performance of white light-emitting diodes (LED).The EQE of the white device based on CzAcSF:30% [tBCzDppy] 2 Cu 4 I 4 was as high as 23.5%, which was one of the highest values among all kinds of solution-processed white devices reported at present, ensuring the practical value of cluster based white LED.
Therefore, we believe that these results and important findings figure out the feasibility of ligand engineering for excited-state optimization and the importance of ligands in energy transfer processes involved in clusters, which can be referable for subsequent researches.The related discussions were added in the revision.Thanks a lot!

Revision:
The discussions on the important findings were add: "Therefore, the incorporation of tBCz groups reduces the gap between optoelectronic properties of blue-emitting TADF host and yellow emissive cluster dopant, which is embodied as the antenna effect of tBCzDppy ligands providing the intermediate energy levels to modulate charge and energy transfer processes.These results demonstrate the superiority of cluster emitters in the diversity and tunability of excited-state characteristics, and the importance of ligand engineering for the controllable optimization." "These results not only demonstrate the superiorities of cluster emitters for practical white lighting applications, but also indicate the flexible manipulation of excited-state properties for cluster molecules and exciton processes in organic-cluster hybrid systems through ligand engineering." 1. Researchers did not conduct any studies to further understand the morphological properties of the synthesized materials.Since the devices were fabricated using solution processing technique, morphology is among the crucial factors affecting device performance and stability.
Response: Thanks a lot for this constructive comment!Accordingly, we measured atom force microscopy (AFM) of spin-coated films for neat clusters and CzAcSF:30% clusters with the thickness of 40 nm, which showed uniform and smooth surfaces with root-mean-square (RMS) roughness less than 1 nm.No device lifetime (T50 and T90) of the fabricated devices were discussed in the manuscript.
Response: Thanks a lot for this constructive comment!Actually, for solution-processed devices, the optimization of carrier injection and transportation are difficult, due to their simple structures with limited carrier transporting layers.
Especially for hole transportation, spin-coated devices commonly only used PEDOT:PSS for hole injection, but did not use hole transporting layers, because spin-coating emissive layers on hole transporting layers can easily destroy the latter and make two layers mixed, leading to electroluminescent performance decrease.Therefore, optimizing the lifetime of solution-processed devices is considerably more time consuming than for vacuum processes because variation of charge transport layers requires the development of cross-linkable materials and careful control of layer morphology.A common strategy is to use vacuum-processable model emitters and realize the resulting, optimized stack with cross-linkable analogues (Angew.Chem.2013, 52, 9563).Therefore, most of CuI based spin-coated devices did not report device duration data (Adv.Mater.2015, 27, 2538).In our work, since no suitable cross-linkable holetransporting materials were commercially available, we also adopted the simple device structures without holetransporting layers.In this case, the long duration time can be hardly achieved.
Nonetheless, we believe that the triplet exciton allocation to [tBCzDppy] 2 Cu 4 I 4 can effectively alleviate exciton accumulation on CzAcSF, therefore elongate device duration.To demonstrate it, we performed aging experiments of the spin-coated devices based on CzAcSF:30% [tBCzDppy] 2 Cu 4 I 4 (Figure C1).The control devices based on neat CzAcSF as emissive layers were also fabricated and measured for comparison.It showed that with the initial luminance of 2000 cd m -2 , the duration time at ~1000 cd m -2 was 0.052 hours for CzAcSF:30% [tBCzDppy] 2 Cu 4 I 4 , which was about seven folds of that of neat CzAcSF based analogs.Thus, it is rational that the values was normal, with a small relative standard deviation less than 5%.The discussion and Supplementary Fig. 30 were added in the revision.Thanks a lot!

Revision:
The histogram of peak EQEs was added:: except Figure S20. Figure S20 itself is very erratic and not following any trend.Even so, no explanation for such uncommon performance observed was discussed.
Response: Thanks a lot for this constructive comment!As summarized in Supplementary Tables 3 and 4 We should apologize for the confusing expressions.As reviewer pointed out, at turn-on voltages, the luminance of some devices was more than 1 cd m -2 .Therefore, the footnotes of Supplementary Tables 3 and 4 about "voltages at 1 cd m -2 " were incorrect, which was revised as "operation voltages for turn on".To avoid operation errors, the devices were firstly measured from 0 V to determine the turn-on voltages, and then formally remeasured from the turn-on voltages with the same voltage intervals.Since the turn-on voltages of the devices were different, the voltage variations of the devices were also diverse.
In Supplementary Fig. 32, since the luminance of BCPO:x% [Dppy] 2 Cu 4 I 4 based devices was very low (about 30 cd m -2 for the maximum), the measurement results were sensitive to operation and unstable.Therefore, the data of BCPO:x% [Dppy] 2 Cu 4 I 4 based devices seemed erratic.Nonetheless, the luminance and efficiencies of the devices still indicated the tendencies of first increase and then decrease.The turning point was at x = 20.
The discussion on operation voltages was added, and footnotes of Supplementary Tables 3 and 4 and Supplementary Fig. 32 were revised.Thanks a lot!

Revision:
Discussion on driving voltages was added, and Supplementary Fig. 30 and tables 3 and 4 were revised: "Compared to [Dppy] 2 Cu 4 I 4 based analogues, [tBCzDppy] 2 Cu 4 I 4 endowed its devices with the lower driving voltages and higher luminance (Supplementary Tables 3 and 4).Therefore, tBCz modification made [tBCzDppy] 2 Cu 4 I 4 involved in electrical processes, and improved exciton formation and radiation." "The devices were firstly applied with bias from zero to find out the turn-on voltages, and then formally measured from the turn-on voltages to minimize operation errors." " [a] Operation voltages for turn on, and at 100 and 1000 cd m -2 " Reviewer #3: General Comment: In this work, the authors selected yellow-emitting copper clusters and a blue TADF host CzAcSF to form the white-emitting devices.Although there were reports of white OLEDs and PeLEDs, I agree with the authors that clusters based on eco-friendly cheap metals can provide the important alternatives for the large-scale applications, since the high rigidity of clusters can limit the J-T distortion of mononuclear complexes.Response: Thanks for this constructive comment!As a bidentate ligand, Dppy can form stable coordination bonds with nearly all kinds of transition metals through its N and P atoms.Furthermore, N-P distance of Dppy unit is ~3 Å.The limited coordination space reduces inter-copper distances, and enhances Cu-Cu interactions and ligand encapsulation of metallic cores.On the other hand, pyridine with electron-withdrawing effect would contribute to electron injection into the clusters; while, introducing an electron-donating tBCz group forms donor-acceptor (D-A) structure for tBCzDppy with enhanced intraligand charge transfer interactions and TADF characteristics, therefore providing energy and charge transfer channels of exciton allocation balance for white emission from host-cluster systems.

Revisions:
The advantages of Dppy over triphenylphosphine were discussed: "With the purpose to enhance Cu-Cu and Cu-I interactions, Dppy unit as planar and rigid pyridine orthosubstituted with flexible diphenylphosphine (DPP) was chosen to form compact bidentate mode, which can form stable coordination with transition metals."

( i )
Ligand engineering modulating excited-state characteristics for yellow Cu 4 I 4 clusters.Different to Cu 4 I 4 cubes reported in our previous works, parallelogram copper clusters formed by N^P ligands in this work reveal the shortened Cu-Cu and Cu-I distances, resulting in their predominant iodine-ligand (ILCT) and metal-iodine-ligand charge transfer (MXLCT) of the first single and triplet excited states of the clusters, which are different from the intramolecular charge transfer in CzAcSF as blue-emitting TADF host, thus avoiding excessive energy transfer and making high doping concentrations of the cluster emitters.(ii)Ligand antenna effect accurately optimizing energy transfer between host matrix and cluster dopants.We introduce di-(tert-butyl)-carbazole (tBCz) group contributing to the high-lying energy levels and pyridine to form a donor-acceptor structured ligand tBCzDppy, which provides a suitable intermediate energy level between CzAcSF host and cluster core to establish the channels for energy transfer and exciton allocation between CzAcSF and 11 yellow-emitting cluster core, leading to white emission combining blue and yellow components from CzAcSF and [tBCzDppy] 2 Cu 4 I 4 at extremely high doping concentration reaching 30%.

Figure C1 .
Figure C1.Comparison on durations of CzAcSF and CzAcSF:30% [tBCzDppy] 2 Cu 4 I 4 based devices.The measurement was performed under constant current mode with initial luminance of 2000 cd m -2 .
, compared to neat CzAcSF based devices, cluster doping markedly increased driving voltages, indicating the dominance of CzAcSF matrix in carrier injection and transportation.Furthermore, compared to [Dppy] 2 Cu 4 I 4 based analogues, no matter CzACsF or BCPO used as hosts, [tBCzDppy] 2 Cu 4 I 4 based devices revealed the lower driving voltages and higher luminance, evidencing the involvement of [tBCzDppy] 2 Cu 4 I 4 in electrical processes and improved exciton formation and radiation via tBCz modification.

Dppy] 2 Cu 4 I 4
and (b) [tBCzDppy] 2 Cu 4 I 4 based spin-coating neat films.Fig. 1 d Proposed mechanisms of facilitated charge (above) and energy transfer (below) between CzAcSF and [tBCzDppy] 2 Cu 4 I 4 mediated by tBCz-contributed energy levels, in comparison to [Dppy] 2 Cu 4 I 4 .Data out and in parenthesis are experimental and simulated values, respectively.5.Supporting Information, page 22, line 177 "tableS2", please provide equations that you used to calculate those rate constants of each photophysics process.

Revision: The corrected table was added: Supplementary Table 1. Physical properties of the clusters.
of [tBCzDPPy] 2 Cu 4 I 4 in common solvents, e.g.chlorobenzene, making device fabrication by solution processing feasible."SupplementaryFig.4| Single crystal structure of [tBCzDppy] 2 Cu 4 I 4 .The brown dash line indicates the centroidcentroid distances of tBCz and Cu 4 I 4 core.7.Supporting Information, page 21, line 171 "table S1", the words "[h] in PMMA matrix" but it is not referred to in the table.Please check it carefully.Response: Thanks a lot for this kind reminding!We should apologize for our carelessness making this mistake.We measured PLQY values of the clusters doped in polymethyl methacrylate (PMMA) films.The corresponding superscripts were corrected.Thanks a lot!

The detailed explanation on energy transfer optimization through cluster emitters was added:
I noticed that Yao et al.recently reported a warm white-emitting device of Cu 2 I 2 clusters with broad emissions, which was obviously different to this work regarding to material design and photophysical investigation (Nat Photon 18,200-206 (2024)).The performance reported in this work was also improved.What I am interested in is the heavy doping for realizing white emission reported in this work, which was thoroughly different to all previously reported white-emitting systems.This finding may discover one advantage of cluster emitters.The authors organized the experiments and investigations carefully to figure out the fundamentals behind the unique photophysical processes in CzAcSF:Cu 4 I 4 cluster films and the key factors of carrier and energy transfer.The EQE of 23.5% achieved at 30% doping concentration by the solution-processed devices indicated the potential of white cluster light-emitting devices.Therefore, I would like to recommend the publication of this work in Nature Communications.Thanks a lot for this constructive comment!Actually, single-emissive-layer white light-emitting diodes attract much attention, since this structure can effectively improve performance repeatability and device stability through minimizing layer numbers and interfaces, among which singly doped single-emissive-layer structures would be "ideal".However, for noble-metal complexes based systems, the doping concentrations of long-wavelength phosphors should be very low to avert excessive energy transfer, markedly reducing the stabilities of color purity, efficiencies and duration for the corresponding white devices.In this case, a feasible strategy is to develop yellow dopants with similar but different excited state properties to the blue-emitting host matrix.According to our previous works, different to mononuclear copper complexes, luminescent copper clusters show unique multi-component excited states due to their more complicated intra-ligand, ligand-metal and metal-metal interactions, in which ligand centered excited states are similar to intramolecular charge transfer excited states of TADF hosts, but cluster-involved excited states are different.In this case, ligand encapsulation and different composition of cluster emitters can be tuned to control the host-guest energy transfer, making heavy doping based white emission feasible.In this work, we demonstrate that through ligand engineering, the ligand based high-lying excited states can serve as the intermediate energy levels to facilitate the energy and carrier transfer from CzAcSF matrix.As consequence, the state-of-the-art efficiencies and high white color purities were achieved by[tBCzDppy]2 Cu 4 I 4 , based on not only singly doped emissive layer structure, but also cluster concentrations as high as 30%.The explanation on superiorities of cluster emitters for white device applications was added in the revision.Thanks a lot! "Ligand-centered (LC) components, especially intra-ligand charge transfer states, are similar to those of phosphors and TADF molecules, but the CC state is completely different.The charge and energy transfer from blue-emitting host matrixes can be facilitated by the former, but limited by the latter, leading to exciton allocation balance.In this sense, through optimizing LC and CC characteristics and ratios in excited states, luminescent clusters would be competent as yellow/orange emitters in singly and heavily doped white light-emitting systems." 2. On page 7, paragraph 3, the authors claimed that the emission duration of [Dppy] 2 Cu 4 I 4 film decreased more significantly at higher temperatures, in comparison to [tBCzDppy] 2 Cu 4 I 4 film, because the rigid and bulky tBCz groups inhibited the quenching effect.Since tBCz groups also modified the solubility and film formability, the film morphology of [tBCzDppy] 2 Cu 4 I 4 might be different with that of [Dppy] 2 Cu 4 I 4 , the authors are suggested to add and discuss the time decay curves of the clusters in powder.Compared with [Dppy] 2 Cu 4 I 4 powder, the variation of emission time decays for [tBCzDppy] 2 Cu 4 I 4 powder is still smaller, along with temperature increasing, which futher verifies the effect of tBCz modification on quenching suppression.The figure and related discussion were added in the revision.
Response:Response: Thanks a lot for this constructive suggestion!Accordingly, we measured the time decay curves of the clusters in powder (Supplementary Fig.13).

Time decays of cluster powders and related discussion were added:
This work reported a novel single-doped white light emission system based on blue TADF host (CzAcSF) and yellow Cu 4 I 4 cluster dopant([tBCzDppy]2 Cu 4 I 4 ).The EL emission changed from cold white to warm white through tuning doping concentration of 20-40%, owing to the limited host-cluster energy transfer.When the doping concentration was 30%, the EQE of the solution-processed devices reached 23.5%.The advantage of singly cluster doped white-emitting device in heavy doping is important for applications.The authors made a systematic investigation and rational explanation on the improved energy transfer between cluster and CzAcSF, through high-lying excited states from carbazole moieties.The authors demonstrated the main conclusions with solid evidences, which would be important to understand the unique excited-state properties of cluster emitters.This work can be published in Nature Communications after suitable revisions.Thanks a lot for this constructive comment!As reviewer pointed out, luminescent cluster materials for monochrome light-emitting devices developed rapidly in recent years, but clusters based white devices were only few.In our previous works, we found that doping yellow-emitting clusters into blue-emitting hosts resulted in either blue or yellow emissions, rather than white emissions, which was even independent on cluster concentrations (Nat.Commun.2023, 14, 2901).The key challenge is that their different excited-state characteristics hinder the host-cluster energy transfer.Compared with pure organic molecules or mononuclear complexes, clusters with multinuclear metallic cores undoubtedly incorporate much more complicated excited states.Nonetheless, it can be noted that multi-component excited states of clusters include intra-ligand, ligand-metal and metal-metal charge transfer states, in which ligand centered excited states are similar to intramolecular charge transfer excited states of TADF hosts, but cluster-involved excited states are different.In this case, ligand centered excited states can serve as the intermediate states to facilitate energy transfer from TADF hosts to luminescent clusterinvolved excited states.This should be based on delicate ligand engineering for optimizing excited-state composition and ratio of the cluster emitters.In this work, through ligand engineering, tBCzDppy based high-lying excited states serve as the intermediate energy levels to facilitate the energy and carrier transfer from CzAcSF matrix.As consequence, the state-of-the-art efficiencies and high white color purities were achieved by [tBCzDppy] 2 Cu 4 I 4 .The description of main challenge in developing cluster based white light-emitting systems was added in the revision.Thanks a lot!
I have noticed that in recent years, there have been some works used clusters as emissive layers to prepared electroluminescent devices, most of which showed blue or yellow emissions, and the reports of white devices based on clusters were only few (Nat.Commun.2023,14, 2901; Angew.Chem.Int.Ed.2021, 61, e202213826).Please briefly introduce the main challenge of developing cluster based white light-emitting devices.Response:

Description of main challenge in developing white light-emitting systems was added:
"Obviously, the key challenge for "ligand-mediated" strategy is how to realize stronger cluster-centered interactions and appropriate ligand functionalization for rationally optimizing excited-state characteristics of the clusters."2.Dppy is a common ligand for cluster preparation.Wang et al prepared gold clusters based on Dppy (J.Am.Chem.Soc.2013, 135, 16184).Therefore, are there any advantages of this kind of ligands in comparison to triphenylphosphine, regarding to EL cluster design.